Vacuum sheet stripping apparatus

ABSTRACT

A vacuum sheet stripping device is herein disclosed suitable for removing cut sheets of final support material from the surface of an image retaining member, as for example, a xerographic plate, and advancing the separated sheet along a predetermined path of travel.

I States Patent [191 Borostyan 1 Nov. 27, 1973 VACUUM SHEET STRIPPING APPARATUS [75] Inventor: Stephen Borostyan, Fairport, N.Y.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

22] Filed: Sept. 16, 1971 [21] Appl. No.: 180,965

[52] US. Cl.....- 271/80, 271/74, 271/DIG. 2,

355/3 [51] Int. Cl. B65h 29/24 [58] Field of Search 271/74, 64, 80, 51,

271/DIG. 2, 27; 355/3 [56] References Cited UNITED STATES PATENTS v 8/1934 Hall et al....., "271/64 40l,790 4/1889 Osborne 271/74 X 3,578,859 5/1971 Stillings..... 3,649,115 3/1972. Hodges 355/3 X FOREIGN PATENTS OR APPLICATIONS 489,351 1/1953 Canada 271/74 1,522,653 11/1969 Germany 355/3 Primary Examiner-Evon C. Blunk Assistant Examiner-Bruce l-I. Stoner, Jr. Attorney-James J. Ralabate [57] ABSTRACT A vacuum sheet stripping device is herein disclosed suitable for removing cut sheets of final support material from the surface of an image retaining member, as for example, a xerographic plate, and advancing the separated sheet along a predetermined path of travel.-

7 Claims, 7 Drawing Figures PATIENTEH SHEEI 1 0F 4 INVENTOR. STEPHEN BOROSTYAN ATTORNEY- PAIENIEUNUVZYIQH SHEET 2 OF 4 m aw m. a

w wt l I This inventionfrelates to 'a vacuumsheet stripping apxaparatus'.jand,.inparticular, to apparatus forseparating a'she'et.ofifinalsupport material from a xerographic plate. f e

."More 'specificallyythis invention relates to a she'et a flow of aeroform fluid over the backside sheet so as to'generate an aerodynamic lift sufficient to elevate at stripping.dev'ice-suitablefor use in an automatic X'eroggraphicsreproducingmachine.In the art. of irerography, asoriginallydisclosed by Carlson in US. Pat. No.

,2,287 ,69.l,.a@xerographic plate,..generally formed of a photoconductive layer a is placed upon a .conductive backing, is .chargeduniformly andthe charged plate tsurfacethen exposed toa. light imageof an original to cbereproduced. Under the influence of the light image, :the photoreceptoris caused tobecome conductive in ahelightstruck regionsso as' toselectively dissipate the electrostatic chargeithereon fAs a result, the original input scene. information is recorded on thefplate in the .formof a latentelectrostatic image. The latent. image 1.is'then made visible-"by contacting the image bearing ",plate surface withi oppositely charged .toner particles which have been specifically developed for this purpose; In general; the. oppositely charged toner particles" coming in contact with the plate are electrostatically 'xattracted intothe charged. imaged regions in proportion to. the amount of charge present so. that the more highly charged regionsonthe plate are developed as relatively idensetoner images while the weakly charged regions aredeveloped-as proportionally less dense images.

The developedzinput scene information recorded on the plate. is. conventionally. transferred electrostatically from the xerographic plate to at final support sheet, suchvas paper or the like,- and the imageaffixed thereto to create a record. of the original. Electrostatic transfer .can take many forms but the 'most widely accepted method'inuse today is that which was originally-dis- .closed by --Schaffert in .U.-S.Pat. No; 2,576,047. In this particular method, asheet of insulatingsupport material is placed directly upon the plate surface with one sideofthecopy sheet incontact with a developed toner I least a portion of the sheet above the plate, and further means to direct the lifted portion of the sheet along a predetermined path of travelinto a subsequent processing station. 7

For a better understanding of these and other objects of the present invention, reference is had to the following' detailed description of the invention to be read in connection with the accompanying drawings wherein:

FIG. l' is a schematic diagram of an automatic xerographic reproducing machine embodying the teachings of the present invention;

FIG. 2 is a partial view in section showing the construction of the vacuum housing and associated drive mechanism forremoving a sheet of final support material from the photoreceptor of the machine illustrated in FIG. 1;

FIGS. 3- 6 are partial section views taken along line 2-2 in FIG. 2 showing the internal construction of the vacuum housing and illustratingthe stepsinvolved in removing final support sheet fromthephotoreceptor and forwarding" the sheet 'toa subsequent processing station;

FIG. 7 is a partial sectional view of the photoreceptor and ,the vacuum. roll illustrating the. mechanism for aerodynamically lifting the leading edgeof the sheet from the photoreceptor surface. V

The apparatus of thepresent invention is shown in FIG. 1 embodied in an automatic xerographic reproducing machine having a xerographic drum 10 formed of a photoconductive surface 1 I placed upon a conduc- -tive backing 12. The drum is supported upon a shaft 13 image supported thereon. The back of the support sheet is treated witha corona discharge to induce a charge. in or on-thesheet'that is capable of-overcoming the forces holdingthe'toner' to the plate and electrostatically bonding the toner particles'to'the-sheet in image configuration.

Removal. of the supportsheet from the image bearing .zplate' surface'has long been a problem in the art because of the delicatenature ofthe finely divided toner image. Prior to fixing,ithe toner imagejis loosely ad- 'hered to the support sheet and, as such, canbe readily .dis'turbed ordegraded when ccntacted'in any manner bysheet'handling meansor the. like.

It is therefore an object of the present invention to provide apparatus for removing sheet material from a support surface without engaging the sheet with me chanical grippers and the like.

'It'is axfurther object of this invention to separate a sheet of final-support material, having a toner image loosely adhering thereto, from a sheet support surface withoutdisturbing the image thereon.

These and otherobjects of the present invention are attained by means of a sheet stripping device suitable for use ina xerographic reproducing machine having a vacuum drawing meanspositioned in fluid'flow communication with the copy sheet capableof producing and arranged to pass sequentially through a series of processing stations as itis moved in the direction indicated.

For the purposes of the present disclosure, the several processing stations in the pathof movement of the drum maybe described as follows:

A charging station A, containing a'corona generating device" 16 being arranged to place a uniform electrostatic charge upon the photoconductive layer of the xerographic drum; Y

An'exposu're station B, wherein a flowing light image of an original supported upon platen 17 is projected onto ther'noving druni surface toselectively dissipate the uniform charge found thereon thus recording the original input scene information on the photoconductor in the'form of a latent electrostatic image;

A developing station C, including a housing 20 containing a quantity of two component developer material and a conveying means 21 adapted to cascade the two component developer material'over the electrostatic image bearing plate surfacewhereby toner particles are attracted into the recorded imaged areas thus rendering the images visible;

A transfer station D, wherein the visible toner image supported on the photoconductive drum surface is transferred from the photoconductor to a sheet of final support material and the sheet then forwarded to a subon the drum surface after the image has been transferred and a housing 26 in which is supported a cleaning member for removing residual toner particles left on the drum after the completion of the transfer operation.

A sheet registering andforwarding mechanism 30 is positioned at the entrance of the transfer station D. The mechanism is arranged to accept individual sheets of final support material from either of two supply trays 31 and 32. In operation, a sheet feeding means 33, associated with each of the supply trays, separates the topmost sheet from a preselected stack and advances the sheet into the registering and forwarding mechanism. Here the leading edge of the sheet is properly registered in relation with the toner image leaving developing station C so that the sheet is advanced into moving contact with the rotating drum surface with one side of the sheet superimposed overthe toner image.

The copysheet and the toner image are advanced in contact together under a pair of parallel aligned corona generators which extend longitudinally across the photoconductive drum surface. The two corona generators 1 include a first transfer corotron 34 and a second detacking corotron 35. his herein contemplated, as is conventional in the xerographic process, that a positively charged latent image is recorded on the photoconductive plate and the image is made visible by ap- 1 is, those areas on the photoconductive surface containing no image information and therefore containing no toner thereon, tend to migrate close to the plate surface and, in turn, induces a negative charge in the photoreceptor. Consequently, a relatively strong attracting force is established between the copy sheet and the drum in the non-imagedplate regions which serves to electrostaticallytack the copy sheet to the drum.v For further information concerning this phenomena reference is hadto Dessauei. and. Clarks text entitled Xerograp hy and Related Processes beginning at page 391.

The second corona generating device 35 'is also positioned within the transfer station opposite generator 34. Generator 35 is a detacking corotron which is adapted to redtice and/or substantially neutralize the electrostatic bond. established between the final support sheet and the photoconductiveplate. Detacking of the sheet is accomplished by inducing a second charge in the copy' sheet which iscapable of counteracting the electrostatic holding forces created during the transfer operation. Corona generator 35 can be of any type capable of attaining this end, however, it is preferred that the detacking corotron be an AC. corona generator adapted to produce emissions sufficient to considerably reduce the bond holding the sheet to the photoconductive surface but insufficientto repel the already transferred toner image back toward the photoreceptor surface. For further information concerning this type of corona generating device, reference is had to the heretofore'mentioned U.S. Pat. No. 3,357,400.

'In operation, the photoconductive drum surface is initially charged at station A to a potential of between +700 and +1 ,000 volts using a corona generator similar to that disclosed by Vyverberg in U.S. Pat. No. 2,836,725 and which operates in a range of between 8.0 micro amps/in. and 13.5 micro amps/in. The operating range of the generator is determined by placing I the exposure and developing steps,the toner image is transferred to a paper support by means of transfer 00- rotron 34. The transfer generator is supported at about 0.25 inches above the photoconductive surface and draws a current of approximately 8.0 micro amps/in. of

- wire. Detacking of the copy sheet is accomplished by means of AC generator 35 that operates in a range of between AC 2.75 to 4.50 micro amps/in. and DC +0.30 to +0.80 micro amps/in. plate current.

Positioned downstream in the direction of drum rotation from the AC detacking corotron is a stationary vacuum manifold housing 36.adapted to partially enclose a rotatable pickup roll member 39. The exposed portion of the pickup roll, that is, that portion of the roll extending exterior the housing, is supported in noncontiguous relation above the rotating xerographic drum surface, preferably between 0.25 and 0.30 inches above the photoreceptor surface so that the. sheets of support material moving in contact with the plate surface passes under the roll in an uninterrupted manner.

The cylindrical vacuum pickup roll member is rotatably supported between the two end walls 47, 51 of the vacuum housing as illustrated in F102 The roll basically consists of a tubular hollow sleeve 40 containing a series of longitudinally aligned pickup slots'62 and a number of parallel aligned circumferential slots 63 formulated therein. One end of the'sleeve,the left hand end as viewed in FIG. 2, is sealed by means of an end cap 43 while the opposite end of the sleeve is placed in fluid'flow communication with a vacuum source (not shown) via a vacuum connector 48 and a hose 66. Circumferential seals 42 and 59 (FIG. 2), as well as drag seals 68 and 69- (FIG. 3), are placed between the housing walls and the roll surface. The seals serve to isolate the interior of; the housing from the'surrounding atmosphere.

End'cap 43 .carries a stub shaft 41 therein and the shaft, in turn, is journaled for rotation. in the left hand wall of the vacuum housing by means of bearing 45. Vacuum connector 48 is made up of two cooperating hollow elements including a fixed member 65 locked to the right hand end wall of the housing, anda movable member 64 press ,fitted into the left hand end of the pickup roll sleevej40. The two cooperating members are movably connected by means of abearing 45 contained within bearing housing 55 thus allowing the pickup roll to freely rotate about its axial centerline. A gear 55 is machined in the movable member 64and the gear arranged to mesh with a drive pinion 53 secured to intermediate shaft 54. A drive sprocket 56 is also affixed to theright hand end of the'intermediate shaft and is operatively connected to the main machine drive system by means of a timing belt (not shown). The surface speedof the vacuum pickup roll is coordinated discrete'chambersi, a'firstmanifold 'chamber'76 and a second sealed chamber "38 which is totally isolated from the surroundingatmosphere: Just prior to the in- I tation of the roll in the direction indicated causes the trailing or body portion of the sheet to be pulled or stripped from the drum surface. Simultaneously there- 7 with; the circumferential slots 63 are carried forward "frorn'beneath'. the drag seal 68 and are positioned in fluid flow communication with the back side of the stripped'portion of thecopy sheet. The negative vac uum pressure created within the pickup roll pulls the body of the copy sheet against the roll at least partially closing the slots 63 and thus securing the trailing portion' of the sheet in contact with the roll surface.

troduction of a copy sheet '70linto the sheet removal zone 71,"'both the longitudinally aligned slots" 62 and the circumferentialslots' 63 formed in the pickup roll surface are positioned within theseale'd chamber 38. The vacuum being drawn "throughthe pickup rolltherefore acts against the closed region-betweensea'ls 67 and 68 and, as a consequence, a maximum head pressure is developed within the system .just p rior to "moving the pickup openings into the sheet liftoff region.

' Further rotationofthe pickup roll surface carries'the longitudinally aligned'pickup openings 62from beneath thedrag sear-68 andpositions the slots 'in non contiguous relation just'behind the leading edge of the copy sheet 70 which, simultaneously" therewith, has been advanced into the-pickup zone 71 'to a'positionas illustratedin FlGzkt'Becauseof the pressure differencev created'between the interior of the pickup roll and the surrounding atmosphere, air is drawn at a" relatively high velocity through 'the' pickup slotsas 'the slots are opened to theatmosphere'ffhis'flowof air, due .tothe fi'positioning of "the pickup slots, is" felt upon the back ing [force in accordance with "'B'ernoullis principle which' issu'fficienttoraise' 'at'lea'st the leading edge por- "tion of the copy sheet 'from 'the' photo'conductive surface arid raise the "sheet towards the'pickup roll. 1 The aerodynamicliftis' considerablyenhanced by reducing or neutralizing the electrostatic tacking forces involved 'in the manner 'previo'usly described. Because of its natural beam strength;*the' leading edge=ofthedetacked support sheet do'es not conform to the arcuate shape of the drum surface' but :r'ather tends :to assume arel'a'tive straight'position as illustrated in FIG. 7 Some finite l'engthof the sheet; a distance designate d (-x) in Further rotation of the roll results in the leading edge of the sheet being pushed over a series of stripper fingers 60 that are secured to' the bottom wall 75 of the stationary manifold 74 thereby separating the sheet from the rotating pickup roll surface. The stripper fing'ers 71 are generally arranged tangentially to the exterior surface of the cylindrical pickup roll and coact therewith to describe a relatively straight path of travel along which the sheets are guided into a fuser assembly 23. As the support sheet is driven over the stripper fingers toward the fuser assembly, the longitudinalpickup slots 62 are carried beneath seal 69 and are broughtwithin the vacuum housing into manifold chamber 74. As a result, the leading edge of the sheet is released and "the manifold region is evacuated causing a negative pressure to be felt at'a series of vacuum ports 76 located along the bottom wall 72 of the manifold. The bottom wall of the manifold is arranged at a slight angle in relation tothe plane determined by the stripper fingers in order to prevent the copy sheet from completely closing ports 76 and thus preventingan excessive drag n r from being exerted on the sheet. In practice, the system side 'ofthe copyfsheet and creates an aero-dynamic liftis designed so that the frictional forces between the surface of the pickup roll 'andthe support sheet, drawn in contact therewith, is always greater than the vacuum forces exerted upon the sheet as it moves along the bottom wall of the manifoldJBymaintaining this force differential,a sheet of support material can beefficiently pushed alongthe stationary transport without danger of the sheet being-damaged due to wrinkling or buckling.

As shown in'FIG. 6,the circumferential slots 63 are arranged to follow the longitudinal slots "62 into the manifold area 74and continuesto holdthe interior of FIG I 7, extends outwardly in abeam-like m'annerfrom the arcu'a'te drum' surface' The length of =the beam cre- "ated is dep'endenton a'nurn ber: of factors which? include i'the detacking process is completedl ln' practicefiit has 1 been found that-a sheet of paper, which has been detackedin the manner herein described, can 'be fficiently removed from the photoconductive surface by e'mploying an average vacuum pressure atthepickup slots ofsom'ewhere 'between 1. 10 and". 1170inches'of,

" water when =the pickup slots are supported at approxi- *mately 0 .030'in'ches"above theback'side bfIhe support sheet.

Under 'the'influ'en'ce o'fthe vacuum pressure the freed -leadi'ng edge of'the sheet is drawn; upwardly into contact' with the s'urfa'ce-of the pickup roll closing 'the lonmoving'roll surface. As illustrated inf FIG. 5,*further rothemanifold'chamber at a negative pressure. During this period, th leading edge of the 'shee'tihas traversed "the-stationary bottom wall of the manifold and moved intothe nip between the cooperating fuser rolls 80 and "81. ln'operation, thefuser rolls are arranged to move at'the same peripheral speed asthe surface speed of the moving's heet. The fuser rolls are adapted in a manner well knownintheartto engage the copy sheet in pressure'driving contact and'herein function to pull the sheet over the stationary wall after the trailing portion of the sheet' is released by the circumferential slots as they are withdrawn within the vacuum housing. As the sheet passesthrough the nip-between the fuser rolls,

sufficientheat energy is transferredto the copy sheet to 'affixthe image'thereto;

"It-should be clear to'one skilled in the art that the diupon the copy sheet as the sheet is moving between the sheet detackingregion and the-fusing region. Further- "more, by properly choosing values for the roll diameter and vacuum slot dimensions, the assembly can be made self-sealing so that a vacuum pressure is only exerted in the pickup region when a sheet of final support material is present therein. During the time that the pickup roll is over an interdocument region, that is, a drum region containing no input scene information, all the .vacuum pressure within the system is directed interior the pickup housing thus preventing the unwanted broadcasting of toner throughout the machine.

For purposes of explanatory convenience, references are made throughout the disclosure to negatively charged toner particles as being used to develop a positively charged latent electrostatic image. It should be understood, however, that the polarity of the charges involved is not intended to limit this disclosure and the polarity of the charges can be altered solong as the specific charge relationships remain constant; All references to positive or negative charges therefore can be considered as defining a relationship. For example, a charged body may be positive or negative so long as the relationship of other like or dissimilar charged bodies is maintained. While this invention has been disclosed with reference to the structure described herein, it is not necessarily confined to the details as set forth and this application is meant to cover all modifications or changes that may come within the scope of the following claims. What is claimed is: g 1. Apparatus for removing a sheet of final support material from the surface of a moving image retaining member, including I a stationary housing being arranged to substantially enclose, in air-tight relationship therewith, a rotatably mounted hollow cylinder having a line of Iongitudinally aligned vacuum ports therein, said housing having an elongated opening positioned 7 adjacent the image retaining member,

means to rotate said cylinder through an endless path of travel whereby the longitudinally. aligned pickup ports pass sequentially through the air-tight enclosed housing and then through the opening therein in close, non-contiguous, relation with a sheet of material supported on the image retaining member, means to coordinate the movement of the cylinder with the movement of the image retaining member so that the longitudinally aligned vacuum ports are brought into the housing opening over the leading edge of a support sheet transported on the image retaining member, and vacuum means operatively associated with said cylinder to draw a flow of air through said ports when said ports are positioned in said housing opening to move a sufficient amount of air over the leading edge of said support sheet to raise the leading edge of the support sheet from the image retaining member into holding contact against said vacuum ports. 2. The apparatus of claim 13 .wherein said cylinder has at least one other secondary opening therein positioned behind said longitudinally aligned vacuum ports in relation to the direction of cylinder movement, said second openings being arranged to engage the trailing portion of said sheet, behind the leading edge thereof, in vacuum holding contact with said cylinder as the leading edge portion of said sheet is carried forward by said cylinder.

3. The apparatus of claim 14 further including stripping means positioned between said stationary housing and said moving cylinder which is arranged to move between the surface of said cylinder and'the support sheet held in contact therewith so as to redirect said sheet away from said cylinder. 1

4. The apparatus of claim 15 wherein one wall of said stationary housing includes an extended surface adapted to co-act with said stripping'means to redirect the support sheet along a predetermined path of travel.

5. Apparatus for removing a sheet of final support material from the surface of a moving image retaining member including a rotatable hollow cylinder having a series of ports therein,

vacuum drawing means operatively associated with the rotatable hollow cylinderfor developinga negative pressure at said ports,

means to rotate said cylinder whereby the ports are transported sequentially through a series of stations including a first station having means to seal said ports whereby a maximumnegative pressureis developed at said ports,

a second pick up station in which said ports are brought into close non-contiguous moving relation with the leading edge of the sheet of support material on the surface of the image retaining member whereby a flow of air is caused to move over the back of the sheet as the air is drawn through said ports to lift the leading edge of said sheet into holding contact against said; cylinder, and

a third sheet stripping station comprising an enclosed vacuum chamber through which said ports are passed, said chamber having one stationary wall cooperating with the rotating cylinder to strip the sheet from the cylinder and guide the sheet along a predetermined path of travel, said wall further having an opening for placing the sheet in fluid flow communication with the vacuum chamber whereby the sheet is held in sliding contact with the wall when said vacuum ports are positioned within the chamber.

6. The apparatus of claim 10 wherein the peripheral speed of said cylinder is substantially equal to the speed of movement of the image retaining member.

7. The apparatusof claim 11 having further sheet guide. means arranged to cooperate with said cylinder to redirect the stripped portion of said sheet along a predeterminedpath of travel. 

1. Apparatus for removing a sheet of final support material from the surface of a moving image retaining member, including a stationary housing being arranged to substantially enclose, in air-tight relationship therewith, a rotatably mounted hollow cylinder having a line of longitudinally aligned vacuum ports therein, said housing having an elongated opening positioned adjacent the image retaining member, means to rotate said cylinder through an endless path of travel whereby the longitudinally aligned pick-up ports pass sequentially through the air-tight enclosed housing and then through the opening therein in close, non-contiguOus, relation with a sheet of material supported on the image retaining member, means to coordinate the movement of the cylinder with the movement of the image retaining member so that the longitudinally aligned vacuum ports are brought into the housing opening over the leading edge of a support sheet transported on the image retaining member, and vacuum means operatively associated with said cylinder to draw a flow of air through said ports when said ports are positioned in said housing opening to move a sufficient amount of air over the leading edge of said support sheet to raise the leading edge of the support sheet from the image retaining member into holding contact against said vacuum ports.
 2. The apparatus of claim 13 wherein said cylinder has at least one other secondary opening therein positioned behind said longitudinally aligned vacuum ports in relation to the direction of cylinder movement, said second openings being arranged to engage the trailing portion of said sheet, behind the leading edge thereof, in vacuum holding contact with said cylinder as the leading edge portion of said sheet is carried forward by said cylinder.
 3. The apparatus of claim 14 further including stripping means positioned between said stationary housing and said moving cylinder which is arranged to move between the surface of said cylinder and the support sheet held in contact therewith so as to redirect said sheet away from said cylinder.
 4. The apparatus of claim 15 wherein one wall of said stationary housing includes an extended surface adapted to co-act with said stripping means to redirect the support sheet along a predetermined path of travel.
 5. Apparatus for removing a sheet of final support material from the surface of a moving image retaining member including a rotatable hollow cylinder having a series of ports therein, vacuum drawing means operatively associated with the rotatable hollow cylinder for developinga negative pressure at said ports, means to rotate said cylinder whereby the ports are transported sequentially through a series of stations including a first station having means to seal said ports whereby a maximum negative pressure is developed at said ports, a second pick up station in which said ports are brought into close non-contiguous moving relation with the leading edge of the sheet of support material on the surface of the image retaining member whereby a flow of air is caused to move over the back of the sheet as the air is drawn through said ports to lift the leading edge of said sheet into holding contact against said cylinder, and a third sheet stripping station comprising an enclosed vacuum chamber through which said ports are passed, said chamber having one stationary wall cooperating with the rotating cylinder to strip the sheet from the cylinder and guide the sheet along a predetermined path of travel, said wall further having an opening for placing the sheet in fluid flow communication with the vacuum chamber whereby the sheet is held in sliding contact with the wall when said vacuum ports are positioned within the chamber.
 6. The apparatus of claim 10 wherein the peripheral speed of said cylinder is substantially equal to the speed of movement of the image retaining member.
 7. The apparatus of claim 11 having further sheet guide means arranged to cooperate with said cylinder to redirect the stripped portion of said sheet along a predetermined path of travel. 